The IEEE (Institute of Electrical and Electronics Engineers) 802.16 standards propose using Orthogonal Frequency Division Multiple Access (OFDMA) for transmission of data over an air interface. OFDMA has also been proposed for use in 3GPP (Third Generation Partnership Project) Evolution communication systems. In an OFDMA communication system, a frequency bandwidth is split into multiple contiguous frequency sub-bands, each sub-band comprising multiple sub-carriers over a given number of OFDM symbols, that are transmitted simultaneously. A user may then be assigned one or more of the frequency sub-bands for an exchange of user information, thereby permitting multiple users to transmit simultaneously on the different sub-carriers.
In order to inform a user, that is, a user's mobile station (MS), of the one or more frequency sub-bands assigned to the user for an uplink transmission, a serving Radio Access Network (RAN) identifies the assignment in a downlink sub-frame that is transmitted to the MS. For example, FIG. 1 is a block diagram of an exemplary frame 100, and in particular a WiMAX frame, of prior art. As depicted in FIG. 1, frame 100 comprises a downlink (DL) sub-frame 120 that is sent by a RAN to users served by the RAN and an uplink (UL) sub-frame 130 that is sent by users to the RAN.
DL sub-frame 120 includes a DL scheduling field (DL-MAP) 124, an UL scheduling field (UL-MAP) 126, and a DL data packet field 128. DL sub-frame 120 further may include a preamble field 122. DL-MAP 114 provides a frame duration, a frame number, a DL sub-band allocation for DL bursts, and a coding and modulation scheme used for each DL burst. UL-MAP 116 provides UL sub-band scheduling for UL bursts by served mobile stations (MSs), a coding and modulation scheme used for each UL burst, and a start time for each UL burst. DL data packet field 128 comprises the DL bursts, that is, is the field in which the RAN transmits data packets to the served MSs based on the sub-band scheduling. Preamble field 122 typically comprises pilots that may be used by MSs for timing synchronization, frequency synchronization, and channel estimation.
UL sub-frame 130 includes a control region comprising a Ranging Code field 132, a channel quality information (CQI) feedback field 134 (that is, CQI channels (CQICH)), and a Hybrid Automatic Repeat reQuest (HARQ) acknowledgement field 136 (that is, HARQ Acknowledgement channels (HARQ ACKCH)). UL sub-frame 130 further comprises an UL data packet field 138. UL data packet field 138 comprises UL bursts, that is, is the field in which the MSs transmit data packets to the RAN based on UL-MAP 126. A location of an MS's data packet in UL data packet field 138, that is, the sub-bands(s) (sub-carriers and times) used by the MS to transmit data, is determined by the assignment received by the MS in UL-MAP 126.
One embodiment of a typical WiMAX communication system is to have a fixed UL-MAP size, such as 100 bytes. Typically, UL-MAPs and DL-MAPs are heavily encoded, and providing scheduling information to an MS requires a non-trivial number of bytes. As a result, when among the MSs being scheduled are many MSs merely requiring a small uplink bandwidth allocation, the size of the UL-MAP can constrain frame utilization, that is, can cause less than full use of the UL data packet field. This is particularly a problem for the UL-MAP where any MS with Best Effort traffic can request a data packet channel allocation, that is, an allocation of one or more sub-bands in UL data packet field 138.
That is, in order to request a data packet channel allocation, an MS randomly picks a Ranging Code and a symbol and conveys this to the RAN in the Ranging Code field 132 of a DL-sub-frame. The Ranging Code and symbol are anonymous and the MS then looks for this Ranging Code and symbol, in association with a bandwidth allocation, in a subsequent UL sub-frame from the RAN. When the RAN gets the Ranging Code, the RAN allocates UL bandwidth, that is, sub-band(s) in UL data packet field 138, to the MS for the purpose of permitting the MS to identify itself and request bandwidth for a particular connection. The RAN then informs the MS, via UL-MAP 126 of an UL sub-frame, of the bandwidth allocated to the MS in UL data packet field 138 for identification and bandwidth request purposes. In response to receiving the allocation, the MS then sends a Bandwidth Request Header, in the allocated sub-band(s) in UL data packet field 138, that requests bandwidth for a particular connection.
The Bandwidth Request Header is a small-size allocation that typically consumes only six to eight bytes. Other similarly small allocations of bandwidth include polls, for example, for a real time polling service (rtPS) or a non-real time polling service (nrtPS), which may occur as often as every 20 milliseconds (ms). When the RAN is engaged in a large enough number of such pollings and/or other small-size bandwidth requests, the UL-MAP 116 can fill up allocating bandwidth to such small bandwidth requests. This can result in a corresponding under utilization of an UL data packet field 138 of a subsequent UL sub-frame.
For example, with an UL-MAP size of 100 bytes and a single slot Code Division Multiple Access (CDMA) information element (IE) comprising eight bytes, the UL-MAP 126 can be completely filled with 12 small bandwidth allocations, whereas Best Effort bandwidth requests also may have been received from some larger bandwidth users. As a result, the RAN may allocate bandwidth in an UL data packet field of an UL sub-frame, such as UL data packet field 138 of an UL sub-frame 130, to 12 small bandwidth users. These 12 users then respectively transmit back to RAN in allocated sub-bands 0-11 of the UL data packet field. A result is that as much as 80% of the UL data packet field is left empty and correspondingly is wasted.
Therefore, a need exists for a method and apparatus that schedules an UL sub-frame in a manner that better utilizes the sub-bands of the UL data packet field.
One of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.